Guest Editorial: Distributed Simulation, Virtual Environments and Real‐time Applications

Welcome to this special issue of Concurrency and Computation on ‘Distributed Simulation, Virtual Environments and Real-time Applications’. The papers included in this special issue are based mainly on selected extended versions of the best papers accepted in the 2007 International Symposium on Distributed Simulation and Real Time Applications (DS-RT 2007). We have only accepted five papers in this special issue from many selected extended versions of papers accepted in DS-RT. This means that these accepted papers have undergone a thorough and a critical review process by experts in the field. In their work Boukerche, Al Hamidi and Zhang described the design and implementation of a web-based 3D virtual environment application that aims to help the training practice of personnel working in the radiology department of a hospital. Their proposed system aims at helping users to learn, to play or to be trained in a ‘like-real’ situation by using X3D technology and embedding it in a distributed virtual environment. Murray, Roberts, Steed, Sharkey, Dickerson, Rae and Wolff addressed an important issue related to collaborative virtual environments and video conferencing. They are enhancing the 3D representation of participants through avatars by mechanisms tracking people's eyes and representing their movements on their avatars. Their approach is capable of reproducing the line of gaze as opposed to approximating it only. They also describe an experiment to assess the difference between users' abilities to judge what objects an avatar is looking at with only head movements being displayed and the eyes remaining static, and with eye gaze and head movement information being displayed. The results from the experiment showed that eye gaze is of vital importance to the subjects correctly identifying what a person is looking at in an immersive virtual environment. Hossain and El Saddik addressed several key issues in distributed multimedia services management and composition such as scalability, heterogeneity and QoS. Their proposed framework introduced biologically inspired multimedia service management through the composition of different multimedia services such as streaming and transcoding services. They make use of biologically inspired algorithms in order to collect the QoS requirements from individual transcoding services that fulfill the requirements of the composition process. A prototype of the proposed framework is designed, implemented and evaluated in terms of scalability and load balancing. Lees, Logan and Theodoropoulos described an optimistic synchronisation algorithm for parallel discrete event simulation of multi-agent systems, and showed that it outperforms Time Warp and time windows on a range of test cases. Their proposed DTRD algorithm uses a decision theoretic model of rollback to derive an optimal time to delay read event so as to maximize the rate of LVT progression. Their analysis suggests that the performance of the algorithm is relatively insensitive to events whose inter-arrival times are not normally distributed. Chetlur and Wilsey described a distributed cancellation mechanism using Total Clocks to prevent cascading and inter-related rollbacks in distributed simulations. The scalability of total clocks is addressed through a time-stamp mechanism referred as plausible total clocks and a proactive cancellation mechanism. They showed that the size of plausible total clocks is dependent on the number of LPs (n) and independent of the number of simulation objects (m) (typically n≪m ). A proof of correctness of the cancellation mechanism using plausible total clocks is then presented to show that only erroneous computations will be annihilated by this technique. Scalability of this technique to track causal relationship makes it suitable for a practical implementation. Mustafee and Taylor introduced WinGrid, a desktop grid computing middleware, specifically designed for executing CSP-based simulations on Windows computers. The authors discussed the use of WinGrid in support of FIRST, a specialist simulation application using the CSP Witness, and the IRS-RBF simulation, a credit risk simulation application using the CSP Analytics. A Grid-enabled version of FIRST and the IRS-RBF simulation has been developed with minimum technological intervention. The performance results of the grid-enabled version of FIRST and the IRS-RBF simulation were presented and discussed in detail. Their work tries to focus attention on the benefit that small desktop grids can give to simulation in industry in the future. I would like to thank all the authors and reviewers for their contributions and devoted efforts. A special thank you goes to the technical program committee of DS-RT for their valuable time and superior work. Thanks are also due to the editorial assistants for their fine support. Finally, special thanks to the Editors-in-Chiefs of Concurrency and Practice for hosting this special issue. I hope that the work reported here will motivate further research and development efforts in this intriguing and vital technology.

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